1) Field of the Invention
The present invention relates to an image forming apparatus that forms an image on a medium such as paper.
2) Description of the Related Art
Japanese Patent Application Laid-Open No. 07-196207 discloses a technique for allowing an optical projector and an optical receiver which form an optical axis that crosses a print paper drawn out from a paper feed tray to detect a quantity of light transmitted through the print paper, converting the detected quantity of transmitted light into a corresponding voltage, comparing the voltage corresponding to the quantity of transmitted light with a predetermined threshold, and determining a type of the print paper. The determination result is then transmitted to a host computer.
Japanese Patent Application Laid-Open No. 09-114267 discloses an image forming apparatus capable of transferring a recorded image onto a recording target material by developing an electrostatic latent image, which the apparatus includes a paper type detecting unit that optically detects characteristics related to a paper quality of the recording target material based on a spectral reflectance, and a control unit that controls transfer of the recorded image according to the detection result of the paper type detecting unit.
Recently, demands for improving an image quality and simplifying operation are increasing for image forming apparatuses. For example, an electrophotographic apparatus is intended to improve image quality by changing a transfer current carried to a transfer device that transfers an image (a toner image) onto paper according to a paper thickness or by changing a temperature of a fixing device. In order to improve the image quality, it is required to strictly control the transfer device, the fixing device, and the like according to information on characteristics of the paper such as a thickness and a color of the paper. Settings of these devices for control, however, all rely on user's manual input.
Nevertheless, in offices, shops, or the like where the image forming apparatus includes multiple tiers of paper feed trays and many unspecified users use various types of paper for the apparatus, the users are reluctant to make such settings as it is complicated, and some users do not know how to handle or how to use the apparatus. Therefore, improvements on image quality cannot be attained in the end.
If the image forming apparatus automatically determines the thickness and the color of the paper as disclosed in the Laid-Open Japanese Patent Applications, the transfer device, the fixing device, and the like can be controlled based on the information on the paper thickness and color.
The techniques disclosed in the Laid-Open Japanese Patent Applications are, however, confronted with the following disadvantages. With each of the conventional techniques, the apparatus can identify only specific items and cannot detect the characteristics of the paper which can be recognized only after two pieces of information, i.e., transmittance and reflectance are detected. As a result, a disadvantage that the transfer device, the fixing device, and the like cannot be controlled based on these pieces of information occurs to the apparatus. Examples of the paper characteristics that can be recognized after the transmittance and reflectance of the paper are detected include a thickness of a colored paper. For example, if the paper color is white only, the thickness of the paper can be determined from the transmittance of the paper. However, if the paper is one of light brown or the other color such as a recycled paper or a colored paper, the paper is lower in transmittance than the white paper even with an equal thickness. As a result, the apparatus erroneously determines the thickness of the paper as thicker than the actual thickness. If not only the transmittance but also reflectance are measured simultaneously, information on the color of the paper can be acquired and the apparatus can, therefore, measure the thickness of the recycled paper or the colored paper as accurately as that of the white paper.